This invention relates to a milling method for the manufacture of components composed of difficult-to-cut materials for turbomachines, aircraft and spacecraft.
A milling method of this kind is known from U.S. Pat. No. 6,077,002. De facto, this patent provides rough machining by so-called full-cut parallel-stroke milling. In this process, a number of laterally offset grooves (rows) are generally milled, the machining of the respectively outermost grooves including the production of the side-wall contours. For this purpose, at least one milling tool which cuts at the tip and at the circumference is used, i.e. an appropriate end milling cutter. Deeper channels, including the multiple lateral groove offset, are machined in a number of feed steps in the longitudinal direction of the milling cutter. The most important area of application for this method are integrally bladed rotor disks, referred to as “blisks” (Bladed Disks), for gas turbines. In the case of the high-strength, difficult-to-cut materials customary for rotors in the construction of gas turbines, the said method has serious disadvantages, such as a low cutting volume per unit time, high tool wear, high costs and thus, ultimately, low economic viability.
Faced with this situation, it is the object of the invention to propose a milling method for difficult-to-cut materials which is clearly superior to the abovementioned method according to all important criteria.
This object is achieved by the claimed features The crucial difference is to be regarded as the fact that, in addition to the centric rotation about its longitudinal centre line, the tool performs an eccentric orbiting motion about a defined orbital axis. The opposite senses of the rotation and the orbiting motion result in downcut milling, which reduces stresses on the tool and the workpiece. Owing to superimposition of a translational advance motion on the eccentric orbiting motion, the path curve of the centre of the tip of the milling cutter corresponds to a cycloid, i.e. to the curve of a point connected firmly to a body rolling on a flat or curved path, it being possible for the radius of the point to be different from the rolling radius. To enable the milling tool to hug non-vertical side walls, i.e. side walls that are not parallel to the orbital axis, in an optimum manner, the axis of the milling tool can be swivelled periodically during each orbit to give a wobbling motion about a defined point on the axis in the region of the tip of the milling cutter, the axis temporarily being parallel to the side wall tangents. With side walls parallel to the orbital axis, this wobbling is not necessary. With the milling strategy according to the invention, it is possible to achieve machining from a solid with finishing parameters, i.e. with a high cutting speed, moderate tool loading, reduced wear and the possibility of a large down feed. The cutting volume per unit time exceeds the known roughing methods many times over, increasing economic viability accordingly.
Preferred refinements of the milling method according to the main claim are reflected in the dependent claims.